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Note-This is not a homework problem,my question is different.I am currently confused understanding some basic behavior in a circuit.Given circuit

Question-Why A is not 10 volts and B 0 volts?What stops Point A from having voltage 10v?

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  • \$\begingroup\$ Because B isn’t grounded. A is 10 V, but only relative to B. Your homework question is asking for voltage A relative to ground. \$\endgroup\$ – winny Feb 4 '18 at 7:07
  • \$\begingroup\$ @winny voltage A is 8.73 ..but still B can be 0 volts even if it is not grounded i solved a similar problem and simulated it too,a bit similar problem. \$\endgroup\$ – Paran Bharali Feb 4 '18 at 7:22
  • \$\begingroup\$ So why did you ask? \$\endgroup\$ – winny Feb 4 '18 at 8:33
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    \$\begingroup\$ @ParanJyotiBharali The 10 V source there is, by definition, maintaining a voltage difference of 10 V between A and B. That means that whatever B is, then A is 10 V higher. And whatever A is, then B is 10 V lower. Period. That's what a voltage source DOES. You cannot have 8.73 V between A and B because you have a voltage source between those two nodes. It makes CERTAIN that there is NOT 8.73 V and instead makes certain that there is 10 V between them. No ifs, ands, or buts. That's what it does. \$\endgroup\$ – jonk Feb 4 '18 at 12:24
  • \$\begingroup\$ @jonk I meant to say that Voltage at A is 8.73 and Voltage at B is 10-8.3 \$\endgroup\$ – Paran Bharali Feb 4 '18 at 16:03
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I think you have a problem understanding the nature of electrical potential. The electrical potential is always measured relatively. That means , if we say a battery is 10V, it is measured with respect to it's negative terminal. When it connected to a circuit the potentials can be different because the current is flowing.

In your question, you are asked to find the voltage with respect to ground,not the negative terminal of the circuit. So you need to apply V=IR to 2ohm resistor and find the voltage drop across it to calculate the potential at B relative to ground. Then 10V is added to the potential of B to find potential at A.

Hope this helps :-)

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Voltage at A is 10V but relative to B! Unless otherwise stated, Voltage at A always refers to voltage w.r.t. ground or zero potential. B itself is not at 0 potential because there'll be some drop in resistance which is connecting it with ground. Thus voltage at A (w.r.t. ground) would be 10V plus the Voltage at B (w. r. t. ground).

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